The present invention relates to electronic devices, and, more particularly, to devices useful for battery charging.
Battery Chargers
The widespread use of battery-powered portable computers (e.g., notebooks, laptops and palmtops) with high performance relies on efficient battery utiliation. In particular, portable computers typically use rechargeable batteries (e.g., lithium, nickel-cadmium, or nickel metal hydride) which weight just a few pounds and deliver 4 to 12 volts. Such batteries provide roughly three hours of computing time, but require about three times as long to be recharged. Such slow recharging is a problem and typically demands that users have several batteries with some recharging while others are being used.
Known battery chargers apply a constant voltage across a discharged battery with the applied voltage determined by the maximum voltage acceptable by the battery. FIG. 1a heuristically illustrates such a battery charger with V.sub.MAX the maximum voltage acceptable by the battery and I.sub.MAX the maximum current; the resistor R and V.sub.MAX are the adjustable values. FIG. 1b is the load line for the battery charger of FIG. 1a and shows the charging current I as a function of the battery voltage V. As the load line shows, the charging current begins at IMAX with a totally discharged battery as indicated by point A. The battery rapidly charges and its voltage increases and the charging current decreases with the operating point moving down the load line as shown by arrow B. Then as the battery voltage rises to near V.sub.MAX, the charging current falls to ero as indicated by point C. And the small charging current implies a large charging time. Indeed, most of the charging time will be during operation approaching point C.
Furthermore, the different chemistries of various battery types preferably use differing recharging voltages, and varying battery capacities (sies) demand differing charging currents. However, known battery chargers cannot automatically adapt to such a variety charging conditions and remain simple to use.
Features
The present invention provides battery charging with charging parameter values selected by communication with imbedded information in a battery pack and then adjusted during charging. This permits adaptation to various battery chemistries and capacities, and, in particular, allows for approximately constant current charging at various current levels and for trickle charging.